The present invention relates, in general, to resistance spot welding equipment and, more specifically, to spot welding electrodes of the male configuration.
Resistance spot welding is a process commonly used to join two thin metal sheets together. A spot weld is produced by clamping two thin sheets of metal together under high pressure or force between two axially aligned electrodes and passing a high electrical current between the electrodes through the metal sheets. The high resistance at the interface of the two metal sheets causes heating of the sheets in an area between the contact surfaces of the electrodes. This rapid heating creates a molten zone of metal which, when cooled, forms a solid weld spot or nugget fusing the two metal sheets together.
The electrodes used to form a spot weld are typically constructed of a high electrically conductive material, such as copper. The size and shape of the electrode determine the size and shape of the spot weld. The electrodes may have an integral single piece form or may be constructed of a holder or shank portion which receives a replaceable cap or tip at one end. The caps or tips are usually of a female or male configuration. The female electrode has an open mounting end whereas the male electrode contains a tapered mounting nipple. The interior of the electrode caps or tips is provided with coolant fluid flow paths for the purpose of removing heat generated by high currents passing through the electrode. Consequently, the more hollow the electrode cap or tip can be made, the more capacity it has to dissipate the generated heat. Currently, the female cap or tip can be made more hollow than the male configuration due to the present design of the latter and the methods employed in its manufacture.
The diameter of the electrode tip, which is generally circular in form, is a critical parameter in producing spot welds of sufficient size to hold two metal sheets together. Thus, depending on the thickness of the two sheets, the electrode pressure, the welding current, etc., the diameter of the electrode is selected to produce a particular diameter weld spot sufficient to hold the two sheets together.
During repeated spot welding operations, the electrodes experience considerable deformation or wear at their contact surface due to the high clamping pressures required and the heat generated by the current passing through the electrode. Such wear or deformation causes the contact surface of the electrode to spread out or "mushroom" which increases its diameter. The increased diameter of the electrode has adverse effect on the spot weld to be produced since less heat is generated at the metal sheet interface due to dissipation of the current flow through the larger contact area of the electrodes. Thus, frequent reshaping or redressing of the electrode tip is required in order to return the tip to its original size and shape. This necessitates interruption of the welding operation which lowers production and increases labor costs since hand machining by file is typically employed to reshape the electrode tip.
Thus, the capacity of an electrode to dissipate the heat generated in the welding process is an important factor in attaining longer electrode life, savings in electrical power consumption, less sticking to the welded material and reduced maintenance cost in the welding operation. It would therefore be desireable to provide a male spot welding electrode with increased cooling capacity in comparison with currently available male spot welding electrodes.